1. Field of the Invention
This invention relates to the field of etching and cleaning processes for MOS devices and, more specifically, to the field of plasma etching and wet chemical cleaning for such devices.
2. Prior Art
In the field of etching processes for MOS circuits a number of methods are known in the art. Each of these methods has its own set of advantages and disadvantages. It is an object of the present invention to derive a process compatible with photoresist masking which allows etching of SiO.sub.2, Si.sub.3 N.sub.4 and oxynitride compounds with end point control, whereby the resulting silicon substrate surface quality yields a high quality and high integrity MOS gate oxide. Further, it is desired to have a reasonable throughput rate when utilizing the process.
One known method of etching semiconductor thin films and dielectrics is a wet etching process. One advantage of such a process is that a relatively high throughput is achieved. However, the method offers poor control of critical dimensions due to the isotropic nature of the process. Also, the method may leave chemical residues which can affect the integrity of oxides grown on the resulting surfaces.
A second well known method of etching employed in semiconductor processing is high power plasma etching, which offers anisotropic etching and relatively high throughput. However, the use of high powered plasma etching results in ion bombardment caused damage such as implanted species, lattice defects and dislocations in the etched surfaces.
Another known method of etching devices is the use of low power plasma etching which reduces the ion bombardment induced damage seen in a high powered plasma etching process. A low power plasma etching process suffers from the disadvantage of longer processing time which limits throughput.
Finally, it is known to use a high power plasma etching process followed by wet etching to eliminate the ion bombardment caused damage and retain some control of critical dimensions. This method introduces added processing steps and complexity and also may suffer from chemical residues on the etched surface.